Be luigi and hit the ? block.
There are two caps in Dire Dire Docks in Super Mario 64. You can find them by going through the underwater tunnel in the first part. It is located to your left when you first come in. After you've gone through the tunnel, head to the surface, and look for the left end of the platform. (Note: you can get both caps at once. Simply get the invisibility cap, and then get the metal cap)
It is in a isolated door in the basement.
you get to bowser's sub then press the ! button the climb the steps to the submarine the get the star
Antima, the cap of invisibility.
A invisibility cap
Hades had an invisibility cap, or helmet.
One symbol for Hades is Cerberus, the three headed dog that guarded the gates of Hades to prevent the dead, who enter on the river Styx, from leaving. Another object that is associated with Hades is the Cap of Invisibility, also referred to as the Helm of Darkness or the Helm/Cap of Hades. The Cap of Invisibility was given to Hades by the Cyclops. They gave it to him as the gave Zeus his thunderbolts and Poseidon his trident. As the trident is Poseidon's main symbol and thunderbolts are Zeus's, the Cap of Invisibility could be considered Hades's main symbol. The Cap of Invisibility allows the wearer to be invisible to any supernatural beings. The cap has a pair of wings on it, attached to each side of the cap.
It goes away after the first mission.
Go as close as you can to the shell and press B to grab it.
It was a cap that made the wearer invisible. It was owned by Hades but worn occasionally by Athena, Hermes, and the hero Perseus
Unless you have a certain number of stars, no room opens when you beat any level. It takes 8 stars to get into "Bowser in the Dark World" 8 stars to get into the "Cavern of the Metal Cap" 8 stars to get into "Vanish Cap under the Moat" 10 stars to get into "Tower of the Wing Cap" 10 stars to unlock the "Big Boo's Haunt" (unconfirmed) 30 stars to unlock "Dire, Dire Docks" The star from Bowser's submarine to get into "Bowser in the Fire Sea"
Nico asked Percy to promise to use Annabeth's invisibility cap for emergencies because he wanted to ensure it was used responsibly and not for frivolous purposes. Nico knows the value and power of the cap and wanted Percy to respect its capabilities.